3 ms·

I was not familiar with the term, so I had to look it up. It's about code like this: a := b the `:=` looks vaguely like a walrus. The most common referenc

by unwind 2y ago

I was not familiar with the term, so I had to look it up. It's about code like this: a := b the `:=` looks vaguely like a walrus. The most common reference language seems to be Python [1]. The usage is for making assignment remain an expression, so you can do stuff like area = (width := get_width()) * (height := get_height()) or something, and have the top-level expression remain valid since the sub-expressions are assignments that remain expressions, i.e. the assigned value is also the result of the expression. [1]: https://realpython.com/python-walrus-operator/ https://realpython.com/python-walrus-operator/

jessekv 2y ago
Its also one of the more controversial features and its introduction sparked Guido's stepping down. Since it was introduced, I have been looking but there has been only a handful of times where I could use it to write clearer code. I'm curious if anyone actually likes it. edit: A quick search shows that I do use it regularly in while loops, e.g.: while result := my_fun(): ...
- miohtama 2y ago
  I have written Python since 2003 and used walrus only once. It's unnecessary.
  - singhrac 2y ago
    Eh, I write a lot of Python and while it's unnecessary, it can make code easier to read if not overused. if (config_fn := base_dir / "config").exists(): ... is just a tiny bit shorter than this: config_fn = base_dir / "config" if config_fn.exists(): ... but if you do this enough times (if you are handling a lot of possible errors / missing data, etc.) it can definitely shorten the code.
    - jessekv 2y ago
      If you have to wrap it in parens, it might be shorter but it's not really clearer. In other contexts, parens are a good indication it's time for a new line. But I can agree something like this does look clean and clear: if value := obj.get("key"): ...
- rich_sasha 2y ago
  IIRC he stepped down because he thought it's a good feature and people pointlessly moaned about it. Not because he thought it's controversial and has enough. I used it a small handful of times. But it also seems like quite a source of footguns. Many examples here: https://github.com/satwikkansal/wtfpython https://github.com/satwikkansal/wtfpython rely on the misuse of the walrus operator.
zem 2y ago
python's use is the unusual one; the most common use (dating all the way back to algol) is to use it for assignment, so you can use = for equality. https://en.wikipedia.org/wiki/Assignment_(computer_science)#Notation https://en.wikipedia.org/wiki/Assignment_(computer_science)#...
- rob74 2y ago
  Go uses "==" for equality checks, "=" for assignments, and ":=" for "declaration/assignment with type inference" - so it's different from both Python (you can use ":=" as part of an expression in Go too, but you can also use "=") and Algol/Pascal (where it's used only for assignment).
weinzierl 2y ago
In math = is used for equality and := for definition[1] which is probably the closest thing to assignment in a programming language. That is why Pascal and similar languages use = for equality only and := for assignment. That always made more sense to me than = for assignment and more =s for different kinds of equality, but in the end this syntax discussions are always just bike-shedding.

by unwind 2y ago

jessekv 2y ago

Its also one of the more controversial features and its introduction sparked Guido's stepping down. Since it was introduced, I have been looking but there has been only a handful of times where I could use it to write clearer code. I'm curious if anyone actually likes it. edit: A quick search shows that I do use it regularly in while loops, e.g.: while result := my_fun(): ...

miohtama 2y ago
I have written Python since 2003 and used walrus only once. It's unnecessary.
- singhrac 2y ago
  Eh, I write a lot of Python and while it's unnecessary, it can make code easier to read if not overused. if (config_fn := base_dir / "config").exists(): ... is just a tiny bit shorter than this: config_fn = base_dir / "config" if config_fn.exists(): ... but if you do this enough times (if you are handling a lot of possible errors / missing data, etc.) it can definitely shorten the code.
  - jessekv 2y ago
    If you have to wrap it in parens, it might be shorter but it's not really clearer. In other contexts, parens are a good indication it's time for a new line. But I can agree something like this does look clean and clear: if value := obj.get("key"): ...
rich_sasha 2y ago
IIRC he stepped down because he thought it's a good feature and people pointlessly moaned about it. Not because he thought it's controversial and has enough. I used it a small handful of times. But it also seems like quite a source of footguns. Many examples here: https://github.com/satwikkansal/wtfpython https://github.com/satwikkansal/wtfpython rely on the misuse of the walrus operator.

zem 2y ago

python's use is the unusual one; the most common use (dating all the way back to algol) is to use it for assignment, so you can use = for equality. https://en.wikipedia.org/wiki/Assignment_(computer_science)#Notation https://en.wikipedia.org/wiki/Assignment_(computer_science)#...

rob74 2y ago
Go uses "==" for equality checks, "=" for assignments, and ":=" for "declaration/assignment with type inference" - so it's different from both Python (you can use ":=" as part of an expression in Go too, but you can also use "=") and Algol/Pascal (where it's used only for assignment).

weinzierl 2y ago

In math = is used for equality and := for definition[1] which is probably the closest thing to assignment in a programming language. That is why Pascal and similar languages use = for equality only and := for assignment. That always made more sense to me than = for assignment and more =s for different kinds of equality, but in the end this syntax discussions are always just bike-shedding.